Added linear regression to compute execution time

[nbacquey]

Uses olsRegress from Statistics.Regression, and adds additional information to the reports and their display. Results on the micro benchmark are strange : some batches have almost perfect confidence, some others are disastrous.

Should be a step in fixing issue #40

[qnikst]

@nbacquey actually it would be nice if you address the comments, but if you want I can take that over can care for the comment and the merge, just tell me.